1. Field of the Invention
The present invention relates to an arrayed-waveguide-grating-type optical multiplexer/demultiplexer having a function of a wavelength multiplexer/demultiplexer that puts together beams of different wavelengths in one or performs division per wavelength, and more particularly to an athermalized (temperature independent) arrayed-waveguide-grating-type optical multiplexer/demultiplexer.
2. Description of the Related Art
In arrayed waveguide gratings (AWG) having an important role as wavelength multiplexer/demultiplexers (multiplexing/demultiplexing), the refractive index of light in quartz glass has temperature dependency, and thus temperature dependency is also seen in the center wavelengths (transmission center wavelengths).
The temperature dependency of center wavelengths of AWGs made of quartz glass is 0.011 nm/° C., and this is a large value not negligible to be used in dense-wavelength division multiplexing (D-WDM) transmission systems.
Therefore, in recent years, for D-WDM transmission systems, which have been progressively diversified, athermalization (temperature independency) of AWGs, which does not require power sources, has been strongly demanded.
Conventionally, in Japanese Patent Application Laid-Open No. 2006-284632, an arrayed-waveguide-grating-type optical multiplexer/demultiplexer (athermal AWG module), which is designed to be athermalized using a compensation plate, has been described (see FIG. 6). An optical multiplexer/demultiplexer 100 of an arrayed waveguide grating illustrated in FIG. 6 has an input waveguide 102 formed on a waveguide chip 114, an input slab waveguide 104 connected to the input waveguide 102, an output waveguide 106, an output slab waveguide 108 connected to the output waveguide 106, and an arrayed waveguide 110 that connects the input slab waveguide 104 and the output slab waveguide 108.
The optical multiplexer/demultiplexer 100 of the arrayed waveguide grating is cut into two at the input slab waveguide 104, to be divided into a first part 116 including one part 104A of the input slab waveguide 104, and a second part 118 including the other part 104B of the input slab waveguide 104.
The first part 116 is connected to the second part 118 by a compensation plate 112. With this configuration, the compensation plate 112 expands and contracts by changes in temperature, and corrects the wavelength shifted due to the temperature changes by moving the one part 104A of the input slab waveguide 104.
With this configuration, light of the same wavelength as that of light input to the output waveguide 106 is able to be output from the input waveguide 102 even if the temperature changes.
However, because in the conventional structure illustrated in FIG. 6, it is required to provide space for sticking the compensation plate 112 on the waveguide chip 114, it is required to consider the space for sticking the compensation plate 112 to determine the shape of the waveguide chip 114. Therefore, the size of the waveguide chip 114 becomes large, the number of waveguide chips 114 that are taken per wafer becomes limited, and thus the manufacturing cost becomes high.